1. Field of the Invention
This invention relates to a method of reading out a color image by scanning the color image with light beams.
2. Description of the Prior Art
In conventional methods of scanning and reading out color images, a white light beam or a laser beam is used for scanning the color images. In the method using a white beam for scanning, the white beam reflected from the original carrying a color image is detected by use of a three-color separation filter and three photomultipliers, or by using a three-color separation filter and a mono-directional solid state image pickup device such as a charge coupled device line sensor (CCD line sensor). However, the method in which the reflected light beam is detected with a three-color separation filter and three photomultipliers is disadvantageous in that it cannot be used for a plane scanning system. On the contrary, the latter method in which the reflected light beam is detected with a three-color separation filter and a mono-directional solid state image pickup device can be used for the plane scanning system. However, commercially available mono-directional solid state image pickup devices have a small number of picture elements and cannot read an image of a large size (like, for example, Japanese B4 size). To read a large size image, it is necessary to connect a plurality of mono-directional solid state image pickup devices and to match the connecting points with high accuracy. This makes it difficult to put the latter method into practical use.
On the other hand, as for the above-mentioned method using a laser beam for scanning, it is known to coaxially superpose an He-Cd laser beam (wavelength 441.6 nm), an Ar laser beam (wavelength 514 nm) and an He-Ne laser beam (wavelength 632.8 nm) for use as the scanning light beam. It is also known to use an He-Ne laser beam only, or to use an Ar laser beam only.
These conventional methods using a laser beam for scanning can be effectively used for the plane scanning system and do not present the above-mentioned difficulty with respect to the manufacture process of the devices. However, the method in which coaxially superposed laser beams are used for scanning is disadvantageous in that three laser sources must be used and, therefore, the method is expensive to conduct, and that the life of the He-Cd laser source is short. On the other hand, the method using only an He-Ne laser beam beam or an Ar laser beam is inexpensive to conduct because it requires only one laser source. However, the method using the He-Ne laser beam only cannot read out yellow and magenta, while the method using the Ar laser beam only cannot read out cyan.